After never seeing a power bill, San Diego families in military housing will start getting invoices for their electricity use later this year.

They won’t have to cover the entire cost. But military families who crank the air conditioning or leave all the lights on — at least 10 percent more than the average user — will owe for the excess.

In Hawaii, the first Navy region to try the power-metering concept in early 2011, about a third of military homes receive a monthly invoice averaging more than $60.

On the flip side, energy-saving households get cash back as an incentive. About a third of Hawaii families use less than the average amount and get monthly rebates averaging $57.

All told, the Navy has cut power use by 10.5 percent in Hawaii. About 15 million kilowatt-hours have been conserved over two years, equaling $3.3 million.

The savings in San Diego is expected to be about the same, though electricity is less expensive here. It will cost $3 million to install power meters in older homes that lack them.

The change is driven by a 1998 Pentagon directive that ordered energy conservation at housing complexes managed by public-private joint ventures — in San Diego County, basically all military family housing constructed over the past decade.

The Army and Air Force have made the switch. The Department of the Navy is following this year all across the continental United States.

Most of the money saved — between 84 percent and 95 percent, San Diego Navy officials estimated — will be rolled back into military housing complexes for maintenance and other projects.

The remaining savings will go to Lincoln Military Housing, the private company that manages the properties.

Historically, families in military housing didn’t get a power bill. The cost was covered as part of their benefits.

In San Diego County, the new policy will affect 9,130 units. Families will get “mock bills” for three months, starting in July. Real billing begins in October. Some homes, including those where the Navy needs to install meters, won’t get bills until February.

The Navy is holding informational meetings around San Diego to inform sailors and their families. Camp Pendleton housing is seeing the same changes, but it is not part of the San Diego program.

Navy wife Melissa Armes received a monthly power invoice in Hawaii, where she lived at Pearl Harbor.

She was in the one-third of families who got money back each month. It was an extra $15 to $30 that helped pay her cable bill, said Armes, who now lives in San Diego in Tierrasanta military housing.

She said she didn’t short her family — husband, three sons and her disabled father — on power use. With boys aged 15, 13 and 10, there are a lot of socks to wash.

“I am not a conservative person. I do what I want, when I want, and I just pay the bill. And even by doing that, I was still getting a check back every month,” Armes said, standing in the middle of her four-bedroom, two-bathroom duplex in a neat military subdivision.

Her family does keep the lights off during the day to make the house cooler for her dad, who is in a wheelchair.

Armes is the contact person — the ombudsman in Navy lingo — for families connected to her husband’s command. She has fielded few questions about the program — the prominent one being whether families with special health issues can be exempted.